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Milky Way Is Twice the Size We Thought
Peter writes to tell us about a research group at the University of Sydney in Australia, who in the middle of some calculation wanted to check the numbers everybody uses for the thickness of our galaxy at the core. Using data available freely on the Internet and analyzing it in a spreadsheet, they discovered in a matter of hours that the Milky Way is 12,000 light years thick, vs. the 6,000 that had been the consensus number for some time.
Yeah, it comes with "%30 MORE!" now.
Obesity is everywhere.
Wikipedia says it's only 1000 light years thick.
This is a good reminder how you're supposed to dig down to the raw data and validate that. I remember reading in one of Richard Feynman's books about a similar case, some conclusion or data appeared well supported, because a lot of the research papers were supportive of the idea, but it turned out that they derived what they said based on a single source.
The case here is similar, it's a good reminder how science is about data, validation and facts not about authority. You're supposed to check your data, check your facts and try to avoid making implicit assumptions.
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[1] Now known to consist of dark matter and dark energy, which is why you can't see them.
1 light-year = 4 * (cost of war in Iraq so far) * (mile/$)
;)
I hope that brings it into perspective for you
For the perfect anti-Unix, write an OS that thinks it knows what you're doing better than you do and let it be wrong.
From TFA with commentary:
Proving not all science requires big, expensive apparatus, Professor Gaensler and colleagues...downloaded data from the internet
No, this actually proves that you can reuse data gathered with large expensive apparatus. There's a difference. They couldn't have done this without expensive infrastructure that just happened to cost them nothing (or close to nothing) - ie. The original instruments and the Internet.
The University of Sydney team's analysis differs from previous calculations because they were more discerning with their data selection. "We used data from pulsars: stars that flash with a regular pulse," Professor Gaensler explains. "As light from these pulsars travels to us, it interacts with electrons scattered between the stars (the Warm Ionised Medium, or WIM), which slows the light down.
Well now wouldn't you want to explore why the data differs so much, before declaring your answer to be the correct one just because you verified your calculations are correct?
My first thought is: Did they use some standard or average value for the density of the WIM? Could the discrepancy be because the WIM itself is not uniform through the thickness of the galaxy/
This is definitely an interesting result and worth following up but rather than declare victory the real question is why is there such a large discrepancy with other data?
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It's pretty hard to measure the size and shape of the Milky Way simply because we are stuck in the middle of it. Measuring the size and shape of far away galaxies is a lot easier because we have a better view. Our galaxy is a flat disk with spiral arms where we are in one of those arms - the overall structure is very hard to measure from that perspective. To complicate things further there is quite a lot if interstellar dust that messes up our view in certain directions.
As an analogy - imagine being stuck in a traffic jam. Figuring out the extent of it is very hard from the view you get from your car. A helicopter in the sky has no problems though.
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TFA says: "The team's results were presented in January this year at the 211th meeting of the American Astronomical Society in Austin, Texas." but there's no indication of where the results have actually been published in a peer-reviewed journal so that one could read the paper for oneself. I looked on the AAS site and couldn't find anything there either. So, pending access to a detailed published per-reviewed account of their work, I'm reserving judgement as to how valid the claim is.
How is this modded "insightful"? Scientific models and methods improve, often building upon earlier models and methods. This isn't an indication of incompetence or malfeasance in the earlier science; it just means that we're getting better at it.
Additionally, the revised estimate of the point of divergence of humans from primates as a result of newly-discovered fossil evidence isn't even remotely relevant to a case in which existing data has been re-interpreted to form a new conclusion.
SIERRA TANGO FOXTROT UNIFORM
Given that Excel is so notoriously inaccurate when doing floating point calculations, I'd be interested if someone else did this in another application. I wonder if they would get the same result.
XML is like violence. If it doesn't solve the problem, use more.
I am an astronomer, so first some background: The Milky way has several components: young stars, old stars, dust and various components of gas. They all have different thicknesses. There is no single "thickness". One of these components (warm ionized gas) has been measured to have a thickness larger than expected. This measurement has not been confirmed by others, nor (I think) published yet.
Despite this complexity, this discussion thread is awash with arguments, confusion, wild speculation, suggestions that dark matter might be wrong etc. etc. OK, fine, this is slashdot, that's what slashdot is for.
But the same people (presumably) have also rushed off to edit Wikipedia! (I see a half dozen edits this morning, to add in the "new" thickness.) That's the part that I find incredible. And people really take Wikipedia seriously?
I agree that the nature of science is that we will definitely need to improve on our findings and get higher and higher levels of accuracy. That is to be expected.
What I find worrying is the range of correction that needs to be applied and also the fact that the correction takes this long - especially considering that the group was able to arrive at a value which is *twice* the older value by just spending a little bit of time studying the data.
The questions it raises are:
1. How is it that the Milkyway was considered to be 6000 light years wide? When someone made this claim, wasn't the data ever rechecked by anyone? If someone with a spreadsheet can come up with this new value of 12000 light years just by spending a few hours studying it, why was it not done earlier? What happened to peer-review - was it ever conducted? If this isn't an indication of incompetence at some level among a few people involved in setting this value, what is?
2. Scientific findings will, no doubt, be modified as new things come to light. However, corrections are normally meant to be just a few % off the initial value. 100% change is not an improvement - it means that the initial value was astoundingly and absolutely wrong. What is staggering about this is the fact that the new value was not calculated based on any *new* finding - but rather it was found just by recalculating based on the *already* existing data.
3. What implications does this have on other findings?
My example about the dating of primate and human evolution was to prove that these type of huge "corrections" have occured even in other scientific fields as well. So what we know to be absolutely true today, can be completely off tomorrow.
It's what happens when one guy does a calculation and everybody else cites it... then it becomes "consensus."
Stupid sexy Flanders.
My example about the dating of primate and human evolution was to prove that these type of huge "corrections" have occured even in other scientific fields as well. So what we know to be absolutely true today, can be completely off tomorrow.
Scientists never know anything to be "absolutely true". Absolute truth is the domain of charlatans, liars and cheats.
When geology started scientists proved that certain rocks in England were "millions of years old!", and postulated based on that that the earth might be "hundreds of millions of years old!". But those numbers seem quaint and even silly today. As new rocks were discovered we soon learned that they were billions of years old, and when we learned about plate tectonics we realized the Earth could be older than the oldest rocks we could find. Our guess as to what the milkyway even looks like are based on looking at other galaxies and then seeing similar structures in our own local neighborhood. We can't actually look at it like we look at other galaxies. We are inside of it; close by stars and dust obscure our view, and our vantage point is that of someone looking at a plane from the side.
What we can see are 'standard candles', that is stars emitting light within a certain range based on our knowledge of nuclear reactions and our ability to calculate apparent mass and composition. This rests on nuclear reaction theory for stars of large mass that we can not test as easily as we can test say simple nuclear decay, and it also rests on a number of approximations for the amount of dust vs "dark matter" in the intervening space (once you know how bright the star is at it's surface, you then base it's distance from you on how bright it appears to you on earth; the stuff in between matters). Terms like "dark matter" and "dark energy" should be hints that we can be off by several magnitudes. If one star is somewhere between 5,000 and 10,000 light years away, while it sounds like a huge difference, the same approximations can tell us that another star is between 5 and 10 light years away.
To put this in perspective, does it really matter if homo split off from ape 1 or 2 or 4 million years ago. Or, whether modern man is 50, 100, or 200 thousand years old? Even what happened in your day yesterday is not completely known to you. You have forgotten most of it, and what you do remember is colored by your dreams last night and your mind's ability to integrate it into what has happened before. But you'll make do with your imperfect knowledge of the day, this month you'll have an idea of how warm it was based on the weather this year + the fact that you don't remember it being an unseasonable day, and ten years from now you'll have an idea based on the season, and ten thousand years from now, people reading your description of your day will have an idea of the weather based on the season and climate. All are less accurate than if I had asked you yesterday how warm it was, but so long as you understand the data and it's approximate accuracy it is still useful. It's useful to have an idea of how long ago ape split off from man vs when modern man split off from other human species, but the day the month and the year isn't important when you're dealing with large numbers like this. The order of magnitude is all you need for any useful work. The processes probably took many years anyway. Except in the laboratory, speciation doesn't happen overnight...
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I fully expect to be modded down to oblivion for this and I honestly couldn't care less.